Reference may be made to the following U.S. Pat. Nos. of interest: 3,671,934; 3,740,713; 3,868,518.
In presently available vehicle alarm systems, unauthorized use of the vehicle is sensed and a siren or other warning device is actuated to provide an audible or visual signal for a predetermined time interval. Typically, in automobile alarm systems, after activating the alarm system to a ready condition, the siren is inhibited by an exit timer for a predetermined time interval, usually about 45 seconds, to allow the user to exit from the vehicle without actuating the siren. In addition, a re-entry timer is provided to enable an authorized user a certain time interval usually about 10-18 seconds, in order to open the car door, enter the vehicle and deactivate the alarm system. Other delay timers may be provided as well.
The requirement for providing various timing intervals in such systems has led to the desire to utilize components of one timing circuit to accomplish more than one timing function. Accordingly, a resistor/capacitor circuit may be used during capacitor charging to inhibit actuation of the siren and thereby provide an exit timing interval, and discharging of the resistor/capacitor circuit may be utilized to provide a predetermined siren actuation or "on" time. Thus, the exit timer interval will be substantially the same as the siren on time, generally about 45 seconds. It is now desired to extend the siren on time for a substantially longer time interval, approaching 3-4 minutes. While the component values of the capacitor and resistor combination could be varied to obtain the desired siren on time, this would undesirably extend the exit time interval to about the same 3-4 minutes. Since an unauthorized user can enter a vehicle very quickly and certainly in less than 2 minutes, it is undesired to inhibit siren actuation for any time period substantially more than the presently desired about 45 seconds.
Accordingly, it is desired to provide a vehicle alarm system in which the siren on time need not correspond to the exit time, and wherein the siren on time can be extended as desired to about 3-4 minutes. Secondly, it is also desired to provide a vehicle alarm system in which such an extended siren on time can be accomplished with a minimum of additional components, if any.